An In Vitro Model of Paroxysmal Supraventricular Tachycardia

Abstract

An in vitro preparation of rabbit right atrium, including the A-V node (AVN) and bundle of His, was utilized to evaluate the mechanism of paroxysmal supraventricular tachycardia (SVT). Microelectrode recordings from atrium and AVN were obtained. During sinus rhythm the atrial cycle was explored with atrial premature depolarizations (APD). Fifty episodes of an arrhythmia with characteristics identical to SVT in man were produced in six of 40 rabbits. In vitro, SVT: (1) was initiated by a single APD showing prolonged conduction in the AVN; (2) had initial cycles similar to atrial echoes; (3) in most instances showed 1:1 A-V conduction; (4) lasted 20 to 500 cycles; and (5) could be ended by a single APD which penetrated the AVN. Reentry in the upper AVN was established by the recording of action potentials from nodal cells which showed marked electrotonic "humps" during repolarization. SVT and atrial echoes could not be produced after damaging or sectioning the upper AVN. An in vitro model of SVT supports the hypothesis that this arrhythmia results from reentry within the AVN.

Longitudinal Dissociation Within the Posterior AV Nodal Input of the Rabbit

“…Initial demonstrations of longitudinal dissociation 3,4,14 and AVNRT 5,6 in the rabbit were assumed to be limited to the AV node. Each study, however, included AN (transitional) cells, Ն4 mm posterior to the compact AV node, as a part of the AV node.…”

“…A minimal mass of atrial myocardium was also suggested as a necessary component for sustained AVNRT. 6 Subsequent studies with superfused rabbit AV preparations by Watanabe and Dreifus 15 and Mazgalev and coworkers 7,8 recognized the role of perinodal fibers in the formation of echo beats and sustained AVNRT. Mazgalev and coworkers 7,8 also described an obligatory role of atrial myocardium superior to the coronary sinus os and tendon of Todaro in AVNRT, stating "in this preparation, AVN reentry circuits always appeared to involve atrial tissue surrounding AVN .…”

“…Further experiments using the superfused rabbit AV junction have demonstrated echo beats and even sustained supraventricular arrhythmia within the posterior-inferior right atrium, with the reentrant pathway contained either within or partially outside of Koch's triangle. [5][6][7][8] Little information concerning the anatomic site and functional basis for echo beats and sustained supraventricular arrhythmia has been provided, a result of a complicated 3-dimensional anatomy and the absence of an accepted definition for the dimensions and location of the AV node. Both the mechanism and the site for AVNRT in humans have been presumed to be intra-AV nodal for 20 to 30 years, with a paucity of clinical data supporting this hypothesis.…”

Paroxysmal supraventricular tachycardia: is the atrium a necessary link?

“…The original mechanism of supraventricular tachycardia described by Moe and Mendez", I included the atrium and a longitudinally dissociated A-V node to form the re-entrant circuit. More recently, Wit et al 23 showed that in the isolated rabbit heart, a small but significant portion of the right atrium was required to sustain supraventricular tachycardia. However, Janse and co-workers,2' using a similar preparation with a plaque electrode over the A-V node, came to the opposite conclusion, i.e., that reentry was entirely subatrial, located entirely in the A-V node.…”

Modulation of conduction and refractoriness in atrioventricular junctional reentrant circuit. Effect on reentry initiated by atrial extrastimulus.

“…Programmed electrical stimulation has proved to be a singularly useful method for study ofreentrant circuits (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Since the original description of this method by Schmitt and Erlanger (1); the conduction characteristics ofthe premature beat have remained the primary focus of studies concerning reentrant circuits.…”